Transcript Pure substances

Unit 1
Structure of Matter
The Known Universe
• Everything in the known universe can be
classified as either matter or energy.
− Matter describes the physical things
around us: the earth, the air you breathe,
your pencil.
− Energy is the ability to cause change or
do work: including light, heat, electrical
energy and mechanical energy, such as
movement.
Matter & Its Properties
• The definition of matter has two parts
− All matter has volume, which is the
3-D space an object occupies
− All matter has mass, which is a measure of
the amount of matter in an object.
Properties & Changes:
• There are 3 common states of matter
− Solids have definite volume & definite shape
o Particles are limited in their movement and packed
close together
− Liquids have definite volume but not definite
shape
o Particles are able to move around each other yet are
still packed close together
− Gases have neither definite vol. nor shape
o Particles are independent of each other
Properties & Changes:
• There are 2 other states of matter that are
not as widely acknowledged
− Plasma is the result of superheating gases
− Supersolid or superfluid is the result of super-
cooling a solid (not much
known about it so far,
but lots of research
possibilities)
Classification of Matter
• All forms of matter (no matter what it
looks like) can be classified into one
of two categories
Classification of Matter
• Two categories:
− Pure substances
o Are uniform in composition
o Described by a chemical formula
− Mixtures
o Are composed of more than one
component blended together
o Different substances physically mixed
together
Classification of Matter: Pure Substances
• A pure substance has a fixed composition
− Every sample has exactly the same
characteristics.
− If they can be separated they can only be
separated by chemical change (elements can
not be broken down further)
− Can be identified by a unique chemical
formula: H, Ar, C, H2O, CO2, CH4, C6H12O6
Classification of Matter: Pure Substances
Methanol
CH4O
Hexane
C6H14
Caffeine
C8N4O2H10
Pure Substances: Atoms
• Atoms are the most basic building blocks
of all matter.
− There are 110+ different kinds of atoms
o All 110+ atoms look identical and are
composed of the same types of pieces
called, subatomic particles
o However, an atom is mostly empty
• There are 3 subatomic particles and they
differ in their location in the atom, their
electrical charge and in their mass
Pure Substances: Atoms
− In the center of the atom is an extremely
dense core called the nucleus, which is
composed of protons and neutrons
o Protons are electrically positive, and make
up half of the mass of the atom
o Neutrons are electrically neutral, and make
up the other half of the mass of the atom
− Surrounding the nucleus is an electrically
negative “particle” called an electron
o We tend to visualize the space the electrons occupy
as a negatively charged cloud
Classification of Matter: Pure Substances
− An element is a pure substance made up of
only one type of atom
− Atoms can combine permanently together
to make up molecules
o A molecule is the smallest version of
chemically combined atoms
− Atoms combine to make up molecules,
atoms and/or molecules can combine to
make up mixtures
Classification of Matter: Mixtures
• Matter that isn’t pure must be a mixture
of pure substances
− The components in a mixture are simply
blended together physically, which means
they can be separated physically
− When pure substances are blended together
the components have the same properties
as when they are separate
o Melting point, boiling point, density, resistance to
chemical change, etc.
Your Turn…
• Classify each of the following as a mixture
or a pure substance
Water
Blood
Table salt
Iron
Brass
Uranium
Wine
Leather
Pure substance
Mixture
Pure substance
Pure substance
Mixture
Pure substance
Mixture
Mixture
Classification of Matter: Mixtures
− There are 2 types of mixtures:
o Heterogeneous mixtures
and
o Homogeneous mixtures
Mixtures: Homogeneous Mixtures
• Homogeneous mixtures are uniform in
composition
− They have the same proportion of
components throughout
− This type of mixture is only composed of a
single phase
o Liquid, solid, gaseous, etc.
− AKA solutions
o For example salt water, brass, air, etc.
o Particle size at the ion, or molecule level, .1 –
2 nm.
Mixtures: Heterogeneous Mixtures
• Heterogeneous mixtures are not uniform
− Often have more than one phase
o gas and liquid, gas and solid, solid and liquid. . .
o e.g. Sea water, granite, blood, sand
Two categories:
①A heterogeneous mixture of large (visible) solid
particles in a liquid is called a
Suspension
o e.g. jar of muddy water, paint, dust particles in air.
o Will settle over time.
o Particle size greater than 1000 nm
Mixtures: Heterogeneous Mixtures
②A mixture of smaller particles that don’t
settle out, but are still visible is called a
Colloid
o e.g. Milk, smoke, fog
o 2-1000 nm
Your Turn…
• Classify each of the following as a
homogeneous or heterogeneous
Soil
The atmosphere
A carbonated soft drink
Gasoline
Gold
A solution of ethanol
and water
heterogeneous
heterogeneous
heterogeneous
homogeneous
homogeneous
homogeneous
Mixtures: Separation Techniques
• All mixtures can be separated by some kind
of physical method
− Mixtures can be separated using several
techniques which have been developed
based on the type of mixture
o
o
o
o
Filtration
Distillation
Chromatography
Crystallization
Separation Techniques: Chromatography
• Chromatography is a technique that works
for separating dissolved solids or a mixture
of several liquids or even gaseous mixtures
− Chromatography makes use of 2 phases
to separate the mixture
o Stationary phase – the phase the mixture is
drawn across, it attracts each component in the
mobile phase differently
o Mobile phase – this phase contains the mix-ture
to be separated; each component flows across the
stationary phase at a unique rate
Separation Techniques: Distillation
• Distillation is an effective method of separating
a mixture of liquids or to purify a liquid with solid
particles dissolved in it
− Uses the differences in the boiling points of
different components in the mixture
− Each component boils at a different temperature,
therefore it is possible to boil off one liquid phase
of the mixture at a time.
• Distillation is used to purify alcohol, or water, or
refine oil
Separation Techniques: Crystallization
• Crystallization is a separation technique,
that produces a pure solid from a solidliquid solution
− Usually involves a
supersaturated solution
o Rock candy, stalactite
and mineral formation,
crystallized honey, etc.
Properties & Changes: Physical
• A physical property is a characteristic that
can be observed or measured without
changing the identity of the substance
− temperature, density, texture, color, shape,
taste, specific heat, strength, luster,
hardness, mass, odor, state, solubility,
conductivity, ductility, malleability, etc.
− It generally takes several phys properties to
identify a substance
Properties & Changes: Physical
• There are 2 types of physical properties:
− Intensive properties, which are properties
that do not depend on the amount of the
matter present.
o Color
o Odor
o Luster
o Malleable
o Ductile
o Conductive
o Hardness
o Melting Point
o Boiling Point
o Density
Properties & Changes: Physical
− Extensive properties, which are properties
that do depend on the amount of matter
present.
o Mass
o Volume
o Area
o Energy
o Electrical Charge
o Momentum
Properties & Changes: Physical Changes
• A change in a substance that does not
include a change in the identity of a
substance is a physical change
− Grinding, melting, cutting, boiling, etc.
• Melting and boiling are part of an important
class of phys changes called changes of
state
− Change from one state of matter to
another (solid to liquid)
Properties & Changes: Chemical Changes
• A property that relates to a substance’s
ability to undergo changes that transform it
into different substances is known as a
chemical property
− Easier to see when substances react to form
new substances. e.g. the ability of charcoal
to burn, ability of iron to rust, ability of silver
to tarnish
• A change in which 1 or more substances are
converted into different substances is called
a chemical change or chemical reaction
(rxn)
Properties & Changes: Chemical Changes
• The substances that react in any chemical
rxn are called reactants
− They are the ingredients
• The results of the reaction are called
products
• An example of a chemical rxn
would be charcoal burning
− Carbon and oxygen would
be the reactants
− Carbon dioxide and water
are the products
Physical vs. Chemical Properties
PHYSICAL
PROPERTIES
CHEMICAL
PROPERTIES
A characteristic of a substance that can
be observed or measured without
changing composition.
Ex: density, color, shape, hardness,
melting & boiling points
2 kinds of phys properties;
Intensive and extensive
The ability of a substance to undergo
chem rxns and to form new substances
Ability to burn, to react, to decompose,
etc.
Your Turn…
• Classify each of the following as physical or
chemical changes
P
C
Moth balls gradually vaporize in a closet
Hydrofluoric acid attacks glass, and is used to
etch calibration marks on glass utensils
C
A French chef making a sauce with brandy is able
to burn off the alcohol from the brandy, leaving
just the brandy flavoring
C
Chemistry majors sometimes get holes in the
cotton jeans they wear to lab because of acid
spills
Properties & Changes: Energy
• When physical or chemical changes occur,
energy is always involved
− Energy is the capacity to do work
• Energy can be released or absorbed
− It is transformed from one type to another,
o Chemical energy stored in charcoal is converted into
heat energy when ignited
• Both energy and matter are conserved
− They can neither be created nor destroyed
− These are called the Laws of Conservation of
Matter & Energy
Properties & Changes: Energy
• We will deal more with energy later, but
there are 8 different types
− Kinetic Energy
− Potential Energy
− *Light Energy
− Sound Energy
− Electrical Energy
− *Chemical Energy
− *Heat Energy
− Mechanical Energy
Pure Substances: Atoms
• The only obvious difference between one
type of atom and another are how many
electrons, protons, and neutrons the
different types of atoms have
Pure Substances: Elements
• Clusters of the same type of atoms are
called elements
− elements are pure substances that can’t
be decomposed
− Each element has features that make it
unique and cause it to behave in a
predictable manner
− They are collectively organized in a huge
chart called the periodic table (PT)
Pure Substances: Elements
• Each square on most Periodic Tables gives
information about the element that the
square represents.
−
−
−
−
Atomic Number
Atomic Symbol
Atomic Name
Atomic Weight
Sec 1-3
Pg 20-24
Pure Substances: Elements
− Atomic Number
o This number is the order that the atom is
on the Periodic Table
o It also represents the number of protons
that the atom has in its nucleus
− Atomic Symbol
o This is the symbolic representation of the
element
o This symbol is used when writing chemical
formulas
Pure Substances: Elements
− Atomic Name
o This is the name of the element, which may
be named from mythology, latin, scientist of
discovery, country of discovery, etc.
− Atomic Weight
o This is a measure of the mass
of the average atom of that element
o It’s equal to the mass of the nucleus of the
average atom of that element
Your Turn…
• Use the clue provided to identify the
element
Atomic number: 5
Symbol: Ga
Atomic weight: 12.011
Symbol: Pb
Atomic weight: 210
Atomic number: 84
Boron
Gallium
Carbon
Lead
Astatine
Polonium
Pure Substances: Organization of the PT
• The PT is organized into vertical columns
called groups or families.
− There are 18 columns
• Each group contains elements with similar
chemical characteristics
− for instance elements in group 2 are
reactive metals with similar abilities to bond
to other kinds of atoms
− Or group 18 which are all gases that are
extremely resistant to chemical change
Pure Substances: Organization of the PT
• The horizontal rows of elements in the PT
are called periods.
− Physical and chem characteristics change
predictably across the period
− Elements close to each other tend to have
similar characteristics, while elements
farther apart become increasingly different
o For example the elements on the far left
of the
PT tend to be soft, shiny solids that are good
conductors
o The far right are gases
Pure Substances: Organization of the PT
• The two sets of elements below the PT
make up what are called the lanthanide
and actinide series.
− They are metallic and radioactive and
should be placed after elements 57 & 89
Pure Substances: Organization of the PT
• There is another major division of the
elements, metals, nonmetals & metalloids.
Pure Substances: Organization of the PT
• A metal is a shiny element that is a good
conductor of heat and electricity
− At room temp, most metals are solids.
o Mercury is an exception, it’s standard state
is liquid (standard state is the state of matter
at 25 C and 1 atm)
− Most metals are also
malleable
o That is they can
be hammered or
rolled into thin sheets
Pure Substances: Organization of the PT
− Metals tend to be ductile.
o Which means they can be drawn into a fine
wire
− Metals behave this way because of their
high tensile strength
o Tensile strength deals with its resistance
to breaking.
o The metal atoms just realign themselves as
the metal is being stretched or hammered.
Pure Substances: Organization of the PT
• Nonmetals are elements that are poor
conductors of heat and electricity
− Many nonmetals are gases at room
temperature (H, O, N, F, Cl)
− One nonmetal is a liquid (Br)
− The rest tend to be brittle solids
(C, S, P, Se, I).
Pure Substances: Organization of the PT
• Metalloids are elements that have some of
the characteristics of metals and some of
nonmetals
− on the stair step line that separates the
metals from the nonmetals
− All metalloids are solids at room temp
− Tend to be less malleable
than metals, but not as brittle
as nonmetals
− Metalloids tend
to be semiconductive
Pure Substances: Organization of the PT
• The elements in the far right column are the
noble gases
− They are unique in that they are generally
unreactive
− All are gases at room temp
− Ne, Ar, Kr, and Xe are all used
in lighting
− Helium is used in party
balloons and weather
balloons